1. Field of the Invention
The present invention relates to a fuel supply system for a boat and an outboard motor, and specifically relates to a fuel supply system for a boat including a fuel injection device for injecting fuel into an intake passage and an outboard motor.
2. Description of the Related Art
Conventionally, a fuel supply system for a boat including a fuel injection device for injecting fuel into an intake passage is known (See, for example, JP-A-2001-140720 and JP-A-Hei 9-88623).
The fuel supply system for a boat described in JP-A-2001-140720 and JP-A-Hei 9-88623 is a fuel supply system for an outboard motor provided on a boat. In JP-A-2001-140720 and JP-A-Hei 9-88623, fuel is pumped up from a fuel tank mounted on a hull and reserved in a vapor separator tank. The fuel reserved in the vapor separator tank is supplied to a fuel injection device by a fuel supply pump. The fuel supply system for a boat described in JP-A-2001-140720 and JP-A-Hei 9-88623 includes a throttle body including a throttle valve for adjusting a flow rate of air supplied to an engine and an intake passage including a plurality of intake pipes, first ends of which are connected to the throttle body and the second ends of which are respectively connected to a plurality of cylinders. The fuel injection device is disposed in the vicinity of a combustion chamber and configured to inject fuel toward a direction in which the air in the intake passage flows (from upstream to downstream).
As in JP-A-2001-140720 and JP-A-Hei 9-88623, in the case where the fuel injection device is disposed in the vicinity of the combustion chamber, it is effective to inject fuel toward a direction of air flow in order to generate a swirl or a tumble in the combustion chamber.
However, in the case where the fuel injection device is spaced from the combustion chamber, if fuel is injected toward the direction in which the air in the intake passage flows, the fuel adheres to a wall surface of the intake passage. Accordingly, it is difficult to spread fuel evenly in the intake passage. Thus, there occurs an uneven distribution of air-fuel ratio in the air-fuel mixture, resulting in deterioration in combustion efficiency of the engine. Specifically, when the configuration in which fuel is injected toward the direction in which the air in the intake passage flows is applied to a configuration in which a single fuel injection device is provided to a plurality of intake pipes of an engine having a plurality of cylinders, the air-fuel ratio of the air-fuel mixture suctioned into each intake pipe fluctuates due to uneven distribution of the fuel, thereby fluctuating the air-fuel ratio of the air-fuel mixture supplied to each cylinder. As a result, it becomes difficult to supply an air-fuel mixture with an appropriate air-fuel ratio evenly to each cylinder, resulting in further deterioration in combustion efficiency of the engine.